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Cardiac arrhythmias caused by a short, hard impact without visible lesions of heart muscle are called Commotio cordis, which can be responsible for sudden cardiac death after chest impact of baseballs and ice hockey pucks in professional sports.
Commotio cordis is believed to be rare, but is one of the most frequent causes of sudden cardiac death among young, otherwise healthy athletes. The risk increases, the smaller and harder the contact is to the chest covering the heart. Previous studies on animals have shown that the window of time during the normal cycle of a beating heart in which Commotio cordis can lead to sudden death is very short indeed: only about 20 milliseconds, or 2% of the normal cardiac cycle.